1. Field of the Invention
This invention relates generally to apparatus and methods used in the design and manufacturing of exhaust header assemblies for internal combustion engines, and more particularly to an exhaust header modeling apparatus and method for designing and manufacturing exhaust header assemblies from typical industry-standard metal tubing sections.
2. Background Art
Development of high performance and racing automobile internal combustion engines requires the design, manufacturing and fabrication of special engine components with specific dimensions and shapes. In some instances, these parts are produced in very limited volumes due to the level of involvement, cost and work required.
Exhaust systems fall into this category, more particularly the tubular exhaust headers, which are custom-made exhaust manifolds of equal length constructed of welded sections of straight and bent metal tubing whose purpose is to achieve higher power output by maximizing the evacuation and scavenging of the exhaust gases out of each individual cylinder of the internal combustion engine. Maximum performance is accomplished through the precise and optimized dimensioning of the individual tubing sections, known as the primary runners, such as the overall length of the pipes, their outside diameter and the wall thickness, among others. These dimensions are critical to meet the specific performance and power requirements set for the particular engine design, and the intended application or applications.
For example, racing teams touring different tracks during a racing season may have to tailor their engines' power curves (and gearbox ratios among other options) specifically for each event. Slow speed tracks require strong mid-range torque engines to exit the turns fast. This particular feature in the power curve of an engine is facilitated by exhaust headers having long pipes or primary runners. On the other hand, high-speed raceways demand high rpm horsepower for sustained constant high speeds, which requires relatively short exhaust header primary runners. Sport exhaust headers sold commercially for street vehicles follow many of these same design principles.
During the actual exhaust header design process, some key dimensions are initially calculated, or inferred from experience, such as the outside diameter and length of the primary runners. Later, after prototypes are built, these parameters may be fine-tuned during actual engine testing sessions on a dynamometer or at the track before the final configuration is obtained.
The construction of these exhaust header prototypes pose a significant challenge to the designer and engine builder. Since the location of the endpoints of the primary runners is usually set and fixed early in the process (for example, one end placed at the exhaust ports of the engine and the other end at the primary runner collector section somewhere in the chassis), exploring the numerous possible pipe pathways between such endpoints can become an overwhelming, time consuming and expensive task. The designer needs to find the optimum pipe layout for each cylinder, which also has to fit precisely in the available space, typically using cut sections of pre-bent tubing commercially available and welding them together.
Many prior art methods exist that attempt to find the best pipe routing. A typical method is to approximate the pathway of the pipes using flexible tubing as a model. Then, the resulting shape is divided into sections than can be obtained from existing pre-bent metal tubing. However, this method is inaccurate because it relies entirely on the precision of manually bending the flexible tubing multiple times (which tends to naturally spring back), to simulate the curves of the actual metal tubing. Imprecision in the bending of the model by hand will render the metal prototype useless as soon as the first mismatch is encountered during the process of welding the actual metal tubing sections.
Another prior art method is to utilize wire to create the ideal centerline of the tubing pathways. This approach not only carries the inaccuracies of the previous method, but also fails to take into consideration the interference that will very likely occur by omitting the volume occupied by the pipes themselves. This situation may result in layouts that are impossible to build.
There are several patents directed toward complex and expensive tube bending fixtures and jigs and apparatus for aligning sections of pipe.
Clark et al, U.S. Pat. No. 4,593,476 discloses a computer aided adjustable tube checking fixture system made up of a template placed on a flat metallic surface, and a series of adjustable holding fixtures places at selected positions along the template. The template has a computer aided layout of a plan view of a formed tube inscribed on a film with selected check points along the layout showing the height and angle of the tubing above the check point. Each holding fixture is adjustable as to height and angle, is indexed to align to the check point, and has a switchable on-off magnet in the base to secure the fixture in position.
Rogers et al, U.S. Pat. No. 4,639,016 discloses a system for repairing pipeline, such as underground fuel, gas or water pipeline systems, which have been damaged by explosives, wherein the ruptured sections have been misaligned. Quick-connect fittings are attached to the misaligned pipe ends after trimming and a bridging conduit system is interposed between the fittings having adjustable portions for accommodating the misalignment. Rotative angular sections provide universal adjustment while retaining the fluid-tight integrity of the apparatus.
Lebourg, U.S. Pat. No. 4,041,720 discloses a method and apparatus for installing a spool between misaligned underwater pipeline sections to effect connection thereof, which is based upon the precise determination of the spatial relation between the pipe ends and the determination of an angle of entry of the spool in a direction to avoid binding between the pipe and spool ends.
The present invention provides a solution that offers the designer a simple way to safely and inexpensively build and modify full-scale 3D models as many times as required before any metal cutting or welding takes place. It also yields the exact dimensions to cut each of the required pre-bent metal tubing sections, and the relative rotation between them when the approved prototype is finally welded together.
The present invention is distinguished over the prior art in general, and these patents in particular by an exhaust header modeling apparatus that includes a plurality of interchangeable straight and curved short cylindrical segment members which are selectively and releasably joined together end-to-end manually and rotated relative to one another to form a full-scale three-dimensional model of a desired engine exhaust header configuration. The segments are provided in sets having outside diameters corresponding to the outside diameters of conventional metal tubing typically used for exhaust heater tubing construction, and have a circumferential scale at each end to visually determine the relative rotation between one segment and an adjoined segment. When completed, the model provides an optimum header pipe layout and pathway for a particular engine that accurately fits within an available space, and provides accurate dimensions to aid in cutting and forming sections of the exhaust headers from pre-bent metal tubing sections. It also displays the proper relative rotation between the sections.